Investigation of nanoprotrusion induced by isolated impact of Ar cluster ion beam on Si and GaAs crystal

Ar cluster was generated by an adiabatic expansion using a converging-diverging Laval nozzle at the pressure 5-7 bar and at room temperature. The size distribution of the cluster was estimated by a time-of-flight (TOF) spectroscopy and the mean size of the cluster at 5 bar was about 500 molecules. Ar cluster was ionized by electron impact and then irradiated on Si(100) and GaAs(100) semiconductor crystal surfaces at the very low fluence to investigate the interaction of cluster with the solid surface. From the isolated cluster impact at the acceleration 15-25 keV, nanoprotrusion with a few tens and hundreds of nanometer diameter and a few nanometer height was observed. This formation of out-grown nano-structure instead of inward crater is predicted due to the increase of the local pressure up to 10-100 GPa and local heating 104-105 K in ps by an impingement of cluster ion beam and re-bounce of liquid medium from the solid and subsequently quenching effect. In addition, the change of Si (100) surface roughness was investigated with the variations of Ar cluster ion dose, and from which phenomenological ESE model of cluster ion impact with solid surface, i.e., surface embossment(E), surface sputtering/smoothing(S), and surface etching(E), is proposed to happen in sequence.